1. Field of the Invention
The present invention relates in general to mounting ophthalmic lenses of a pair of eyesight-correcting eyeglasses on a frame, and it relates more particularly to a method and a device for preparing the lenses of a pair of eyeglasses for mounting on the frame selected by the wearer, and including means for performing an overall contactless optical measurement of a local optical characteristic of the lens, in combination with feeler means.
2. Description of the Related Art
Various measurement devices are known that operate either automatically, or manually, for measuring and detecting various characteristics of a single-vision or a progressive ophthalmic lens before or after it has been mounted on a frame, and in particular its power and centering or identification, and to do so without making contact, by performing optical analysis to produce an overall map. In particular, one such device is known from document FR-2 825 466 equivalent to US-2003/0015649 published on Jan. 23, 2003. In that kind of measurement device, the lens is presented between illumination means and analysis means in order to obtain a map of one or more of its optical characteristics. The optical map may be obtained by deflectometry (of the Hartmann, moire, etc. type) as in the above-mentioned document, or by interferometry, by wave propagation, etc. The user interface can then display not only the optical center or reference, but also maps of power and/or of powers and/or axial direction in one or more remarkable points of the lens.
The advantage of that type of contactless overall optical measurement device operating by mapping analysis lies in its flexibility in use and the way in which it can be automated.
However a major drawback of that kind of measurement device lies in its relative lack of accuracy, in particular when measuring local powers. Performance in terms of accuracy is clearly degraded, in particular in comparison with devices for performing localized measurements by means of an endpiece, of the frontofocometer type.